This invention relates to release liners for supporting adhesive tapes, more particularly, to release liners which provide significant roll stability to narrow rolls of adhesive tape and, even more particularly, to release liners which provide significant stability to narrow rolls of double-sided adhesive tape, where the tape has a heat activated adhesive side and a pressure sensitive adhesive side. This invention also relates to such release liners in combination with an adhesive tape.
Adhesive tapes have been useful in a variety of industrial and automotive applications. Double sided adhesive tapes have been used to bond together a variety of substrates or surfaces and are particularly useful for industrial and automotive applications. Double-sided adhesive tapes having a heat activated adhesive (HAA) side and a pressure sensitive adhesive (PSA) side (e.g., in the form of a foam core with a heat activated adhesive on one side and a pressure sensitive adhesive on the other side) have been found useful in bonding together substrates of dissimilar materials. For example, such tapes have been used to attach a rubber-type substrate (e.g., thermoplastic and thermoset olefinic elastomeric materials) to a metal or a painted metal surface. In particular, such attachment tape has been used to attach rubber-type weatherstrip to the painted metal surface of a vehicle. In such an application, the PSA is bonded to the painted metal surface and the HAA is bonded to the rubber-type substrate. Polyethylene (PE) and polypropylene (PP) materials have been used for the HAA, and acrylic adhesives and tapes (e.g., in the form of a foam core and adhesive) have been used for the PSA. Acrylic adhesives generally have excellent adhesion to metal and painted metal surfaces but generally do not bond well to rubber type materials. Heat activated adhesives such as, for example, polypropylene and ethylene acrylic acid copolymer containing materials have been used for bonding an acrylic adhesive layer to rubber-type materials.
Such double-sided attachment tapes are typically manufactured in wide sheets, laminated onto a release liner of matching width to form a tape assembly, and then wound into a roll. Such liners include a release side which is bonded to the PSA side of the tape during the lamination step. The liner is chosen to have a release side that is bondable to yet readily removable from the PSA side of the tape. One such liner that has been used in the past has an outer layer of high density polyethylene (HDPE) with a thickness of about 0.5 mils (0.0127 mm), a center layer of medium density polyethylene (MDPE) with a thickness of about 3 mils (0.0762 mm), and a second outer layer of low density polyethylene (LDPE) with a thickness of about 0.5 mils (0.0127 mm). The resulting wide roll of the tape assembly is then converted or separated (e.g., by slitting) into a plurality of narrower rolls of the tape assembly having the same width or varying widths, depending on the intended use(s) of the tape. For example, tape widths of about 0.5 in. (1.27 cm) or less have been used to bond weatherstrip to automobile door frames. The liner is left intact while the HAA is laminated to the weatherstrip using heat and pressure. The liner is then removed and the resulting weatherstrip composite is bonded to the auto body frame using the PSA side of the tape.
One problem encountered in the past has been the instability of narrow rolls of such tape assemblies which are made with tape having a HAA side and a PSA side. Since the PSA side is protected by the release liner, and not exposed, it is the HAA side that contacts the release liner, not the PSA side, when the tape assembly is wound into a roll. The coils or layers forming these prior narrow rolls have tended to slip and slide relative to one another, causing the roll to telescope and come apart. As a result, the diameter of such unstable narrow rolls has had to be limited because larger diameter rolls come apart easier. In addition, even such unstable narrow rolls with smaller diameters have had to be handled with great care to prevent them from coming apart. Such handling measures have included mounting the slit side of the narrow roll onto a support wafer (e.g., made of a high density polyethylene). The support wafer is then carried like a plate to support and prevent coils of the narrow roll from telescoping apart. Thus, the use of narrow rolls of such tape assemblies has been cumbersome, time consuming and costly.
Therefore, there is a need for a release liner which provides more stability to narrow rolls of adhesive tape assemblies containing tape with a HAA side and a PSA side.
The present release liner provides more roll stability (i.e., the coils forming the roll are less likely to fall apart when the roll is held suspended along its outer circumferential edge) when used with double-sided tape having a heat activated adhesive (xe2x80x9cHAAxe2x80x9d) side and a pressure sensitive adhesive (xe2x80x9cPSAxe2x80x9d) side. In this way, the present invention satisfies the need for more stable rolls, especially more stable narrow rolls, of adhesive tape assemblies containing tape with a HAA side and a PSA side.
In one aspect of the present invention, an adhesive tape assembly is provided which comprises a double-sided adhesive tape and a release liner according to the teachings of the present invention. The tape includes a front adhesive side comprising a HAA layer of a heat activated adhesive and a back adhesive side comprising a PSA layer of a pressure sensitive adhesive. As used herein, xe2x80x9cheat activated adhesivexe2x80x9d refers to an adhesive that bonds to a contacting substrate or other surface when enough heat is added to the adhesive. The release liner includes a front liner side comprising a release layer in contact with, bonded to and readily removable from the PSA layer and a back liner side comprising a roll stability layer. The roll stability layer comprises an ethylene vinyl acetate and contacts the HAA layer when the adhesive tape assembly is formed into a roll. The roll stability layer is also operatively adapted to provide the adhesive tape assembly with a substantial increase in roll stability when formed into a roll of narrow width.
The HAA layer has a contact surface which contacts the roll stability layer when the adhesive tape assembly is formed into a roll. It is desirable for the contact surface to have a smooth, shiny or glossy finish. Surprisingly, such a smooth, shiny or glossy finish on the contact surface of the HAA layer appears to improve the coefficient of friction between the contacting surfaces of the HAA layer and the roll stability layer. Even so, the adhesive tape assembly may also exhibit improved stability with the contact surface of the HAA layer having a matte finish.
The release layer may comprise any material suitable for functioning as a release layer for a pressure sensitive adhesive and being bondable to the roll stability layer. Alternatively, the surface of the release layer, in contact with the PSA layer, may be coated with a release material such as, for example silicone or fluorocarbon. However, it may be desirable to avoid the use of such release materials to avoid contamination by this material.
It is desirable for the roll stability layer to comprise an ethylene vinyl acetate (xe2x80x9cEVAxe2x80x9d) that has a low enough vinyl acetate (xe2x80x9cVAxe2x80x9d) content to prevent the roll stability layer from blocking with the HAA layer. It is also desirable for the ethylene vinyl acetate to have a high enough VA content to obtain a coefficient of friction between the roll stability layer and the HAA layer that maintains stability of a roll of the adhesive tape assembly.
It is desirable for the roll stability layer to comprise an ethylene vinyl acetate having a vinyl acetate content of less than about 28% by weight. It is also desirable for the ethylene vinyl acetate of the roll stability layer to have a vinyl acetate content in the range of greater than about 5% up to about 24% by weight. It is further desirable for the ethylene vinyl acetate of the roll stability layer to have a vinyl acetate content in the range of about 8% to about 20% by weight.
It may also be desirable for the roll stability layer to include an anti-blocking agent (e.g., diatomaceous earth, clay and talc) in sufficiently low amounts so as to not significantly affect the coefficient of friction of the roll stability layer, when measured against the HAA layer.
It is believed that roll stability for the adhesive tape assembly can occur when the roll stability layer has a coefficient of friction of at least about 0.55, when measured against the HAA layer. It is also believed that roll stability can occur when the roll stability layer has a coefficient of friction of greater than about 0.5, when measured against the HAA layer. It is further believed that roll stability can occur when the roll stability layer has a coefficient of friction greater than about 0.4, when measured against the HAA layer.
When the adhesive tape assembly has an overall thickness of about 0.052 inches (0.132 cm) and is wound into a roll, with the roll stability layer contacting the HAA layer, the roll exhibits roll stability (i.e., the coils forming the roll do not substantially telescope or fall apart when the roll is held suspended along its outer circumferential edge) even when the roll has a diameter that is at least about 20 times the width of the adhesive tape assembly. This is the minimum diameter to width ratio at which roll stability problems have been experienced with rolls of prior adhesive tape assemblies comprising a double-sided adhesive tape, with a HAA side and a PSA side, and a release liner releasably bonded to the PSA side.
In another aspect of the present invention, an adhesive tape assembly is provided which includes a double-sided adhesive tape and a release liner. The tape includes a front adhesive side comprising a HAA layer of a polyolefin heat activated adhesive and a back adhesive side comprising a PSA layer of a pressure sensitive adhesive. The release liner includes a front liner side and a back liner side. The front liner side comprises a release layer, which is in contact with, bonded to and readily removable from the PSA layer. The back liner side comprises a roll stability layer, which contacts the HAA layer when the adhesive tape assembly is formed into a roll. The roll stability layer has a contact surface which has a coefficient of friction, when measured against the HAA layer, which provides a substantial increase in roll stability (i.e., the coils forming the roll do not fall apart when the roll is held suspended along its outer edge) to a narrow width roll of the adhesive tape assembly
In a further aspect of the present invention, a release liner is provided for use with a double-sided adhesive tape having a front adhesive side comprising a heat activated adhesive layer and a back adhesive side comprising a pressure sensitive adhesive layer. The release liner includes a front liner side comprising a release layer having an exposed contact surface bondable to and readily removable from the pressure sensitive adhesive layer; and a back liner side comprising a roll stability layer. The roll stability layer comprises an ethylene vinyl acetate and is operatively adapted (e.g., formulated) to provide a substantial increase in stability to a narrow width roll of an adhesive tape assembly formed by releasably bonding the release layer to the pressure sensitive adhesive side of the double-sided adhesive tape and then winding the resulting adhesive tape assembly into a roll.
The objectives, features, and advantages of the present invention will become apparent upon consideration of the present specification and the appended drawings.